The present invention relates to tools for cutting grooves in ductboard and, more particularly, to hand tools for cutting grooves in ductboard.
Fiberglass ductboard is typically utilized for the construction of air ducts. The fiberglass ductboard arrives at construction sites in four foot by eight foot, four foot by ten foot, or eight foot by eight foot panels. Grooves are then cut into the ductboard so that the ductboard may be bent and shaped into box-like air ducts.
Fiberglass ductboard is typically one inch or one and one-half inches thick and includes an aluminum foil or staple flap layer on one side. Grooves are often cut in the fiberglass within 1/16th of an inch of the foil layer, or right down to the foil layer without a piercing of the foil.
A standard fiberglass cutting tool for cutting grooves in ductboard typically includes two blade portions lying transversely of each other. In the cutting process, the blades may be forced apart such that the cut groove is imperfect with odd pieces of ductboard that are chiseled out.
Three different forces may cause the transverse separation which results in the incomplete cut. One force may be the horizontal grain of the fiberglass ductboard that runs along or generally parallel to the plane in which the ductboard lies. Ductboard is formed of planar sheets of fiberglass which in the final product form an undulating pattern while running generally parallel to the plane of the board. The blades tend to follow the grain and be drawn toward and away from a surface of the ductboard. When the blades are drawn as such, the blades also deflect or swing transversely as they are fixed relative to the tool. The deflection or separation of the blades causes the incomplete cut.
Another force that may cause such an incomplete cut is the beveled feature of the cutting edges on the blades. The beveled cutting edge may act like a frontwardly disposed rudder permanently fixed to steer the blades transversely apart from one another.
A third force is the deflector tab as shown and described in the parent application Ser. No. 444,534 filed Dec. 1, 1989. As the extractor tabs direct a scrap strip of ductboard from the groove, the strip brings a return pressure to bear on the tab which may cause deflection or separation of the blades.